Federal Communications CommissionFCC 01-60
Before the
Federal Communications Commission
Washington, D.C. 20554
In the Matter of )
)
An Inquiry Into the Commission's)
Policies and Rules Regarding AM)MM Docket No. 93-177
Radio Service Directional Antenna)RM-7594
Performance Verification)
REPORT AND ORDER
AND
FURTHER NOTICE OF PROPOSED RULEMAKING
Adopted: February 14, 2001Released: March 7, 2001
Comment Date: 75 days after publication in the Federal Register
Reply Comment Date: 135 days after publication in the Federal Register
By the Commission:
Table of Contents
HeadingParagraph #
1
Federal Communications CommissionFCC 01-60
I.Introduction...... 1
II.Directional Antenna Proofs of Performance...... 3
A.Full Proof of Performance...... 4
1.Number of Radials...... 4
2.Number of Points per Radial, Length of Radials...... 8
3.Standard Format for Reporting Measurements...... 12
B.Partial Proof of Performance...... 13
1.Number of Radials Required, Number of Points per Radial...... 14
2.When Required...... 17
C.Monitoring Points...... 19
III.AM Station Equipment & Measurements...... 26
A.Base Current Ammeters...... 26
B.Antenna Monitors...... 29
C.Impedance Measurements Across a Range of Frequencies...... 32
D.Common Point Impedance Measurements...... 34
IV.Designation of Critical Arrays...... 36
V.Conclusion...... 42
VI.Further Notice of Proposed Rulemaking on the Use of Computer Modeling...... 43
to Predict Antenna Performance
VII.Administrative Matters...... 48
Appendix A...... List of Commenters
Appendix BFinal Regulatory Flexibility Analysis
Appendix CInitial Regulatory Flexibility Analysis
Appendix D...... Rule Changes
I.Introduction
1
Federal Communications CommissionFCC 01-60
1. This Report and Order and Further Noticeof Proposed Rulemaking (Report and Order) is part of a broad-based streamlining initiative to overhaul Mass Media Bureau policies and licensing procedures. In the course of this initiative, the Commission has introduced substantially shorter and simpler certification-based application forms, established new broadcast application licensing procedures, and instituted electronic filing.[1] This Report and Order reduces the regulatory burdens on AM broadcasters using directional antennas by relaxing our technical rules to the extent possible while still maintaining the integrity of the service. There are approximately 1,900 directional AM stations presently licensed in the United States. Directional AM stations use antennas which suppress radiated field in some directions and enhance it in others. In order to control interference between stations and assure adequate community coverage, directional AM stations must undergo extensive "proofs of performance" to demonstrate that the antenna system operates as authorized. The field strength measurements and technical exhibits which our current rules require as part of a “proof” impose a substantial financial burden upon these AM broadcasters, a burden not incurred by licensees in the other broadcast services.[2] This Report and Order substantially reduces this burden.
2.This proceeding began with a Notice of Inquiry in response to a joint petition for rulemaking filed by five broadcast consulting engineering firms ("Joint Petitioners")[3], which argued that the Commission could materially reduce the measurement burdens imposed on AM broadcasters, based on certain technological advances. The Joint Petitioners requested a thorough examination of these rules and the adoption of alternate means of directional antenna system verification. The Commission subsequently issued a Notice of Proposed Rulemaking ("NPRM")[4] seeking comments on the incorporation of new techniques for AM analysis into our rules, and on our proposals to streamline existing requirements. In response to the NPRM, the Commission received 18 comments and four reply comments.[5] In general, the comments and reply comments share the view that rule changes are warranted to reduce the burdens of verifying AM directional antenna patterns. This Report and Order adopts most of the streamlining initiatives proposed in the NPRM. We are confident that relaxing our proof requirements will provide meaningful relief to many AM broadcasters without jeopardizing technical standards or service to the public. However, we believe it is premature to take any action on the use of certain computer modeling methods to verify directional stations’ operating parameters. We also seek additional comments on these methods.
II.Directional Antenna Proofs of Performance
3.An antenna proof of performance establishes whether the radiation pattern of an AM station is in compliance with the station's authorization. An AM station must perform a full proof to verify the pattern shape when a new directional antenna system is authorized. Partial proofs, which require fewer measurements, are occasionally necessary to show that an array continues to operate properly. For both full and partial proofs, we proposed to reduce both the number of radials and the number of measurements per radial. Nearly all commenters agreed that proof requirements could be relaxed without compromising the technical integrity of the AM service.
A.Full Proof of Performance
1.Number of Radials
4.Background. Under the Commission’s rules, a permittee must measure a minimum of eight radials in a proof of performance.[6] For complex patterns, measurements are required on a sufficient number of radials to define the pattern shape completely, i.e., three radials in the main lobe, and one in each null and minor lobe. In the NPRM, we proposed to reduce the minimum number of radials required from eight to six for simple directional antenna patterns and, generally, to require no more than 12 radials to define complex patterns. The radials would be distributed as follows:
(a)One radial in the major lobe, at the pattern maximum.
(b)Five additional radials, and others as necessary to establish the pattern clearly. These radials will be generally at the peaks of minor lobes and at pattern nulls. This may include radials specified on the station's authorization. However, no two radials may be more than 90 azimuth apart. If two radials would be more than 90 apart, then an additional radial must be specified within that arc.
(c)Any radials specified on the construction permit or license.
5.Nondirectional antenna measurements would be taken along the radials used for directional measurements. In addition, we proposed that those few nondirectional stations which are required to conduct a full proof (due to the proximity of reradiating structures, or other atypical circumstances) should also be permitted to employ six evenly spaced radials, in lieu of eight.
6.Most commenters support a reduction in the number of measured radials. Some suggest that the number of required radials could be reduced even further than we proposed. Hatfield & Dawson, DLR, and Sellmeyer Engineering (Sellmeyer) argue that marketplace considerations will ensure adequate performance, and therefore, that major lobe measurements are unnecessary. Hatfield & Dawson also suggests that, for simple patterns with a single null, “three or four radials may be used.” The Walt Disney Company (Disney) expresses similar views, stating that “[a] two-tower ‘cardioid’ array …could be defined by two radials, and other two-tower arrays by as few as three radials.” Clear Channel Communications, Inc. (Clear Channel), DLR, and Sellmeyer agree that fewer than six radials would suffice for simple patterns. Most other commenters support our proposed minimum of six radials with a maximum span of 90 degrees between radials. According to Carl T. Jones Corporation, “complex designs may result in critical shaping of the pattern…without resulting in more than one pattern minim[um].”
7.Discussion. We will adopt the proposed minimum of six radials, including one radial in the major lobe and a 90 maximum span, to provide the best balance between reducing the burden of proof measurements and ensuring proper array performance. While we recognize that the null structure of simple patterns can be defined with a few radials, we believe that additional measurements are necessary to ensure that the array meets two critical Commission requirements: antenna efficiency and principal community coverage.[7] Marketplace considerations alone will not ensure that these requirements are fulfilled. As proposed, we will limit the maximum number of radials required to 12, allowing use of symmetry for complex patterns which might otherwise require more than 12 radials to define all pattern features.
2.Number of Points per Radial, Length of Radials
8.Background. A full proof establishes field strengths along each radial on the basis of 20 to 30 measured points. We proposed to reduce the number of points per radial to a minimum of 15 directional points, as well as to shorten the minimum length of the radial to 15 km. We proposed to specify intervals between these points as follows:
(1)The closest point at a distance ten times the maximum distance between the elements of a directional array, or at a distance five times the vertical height of the antenna in the case of a nondirectional station;
(2)Close-in measurements at intervals of approximately 0.2 kilometer, out to a distance of three kilometers, with a minimum of seven nondirectional points (added);
(3)Measurements at intervals of approximately one kilometer between three and five kilometers (three points);
(4)Measurements at intervals of approximately two kilometers between five and 15 km (five points);
(5)Additional measurements as necessary at greater distances to achieve at least 15 points clear of potential reradiating structures; and
(6)Measurements at any monitoring point locations along the radial (unchanged from the present rule).
9.Discussion. Commenters unanimously support a reduction in the required number of points and the length of the radials. We agree with Carl T. Jones Corporation, which notes that nondirectional measurements begin closer to the antenna site than directional measurements; consequently, a proof includes more nondirectional points.[8] These additional nondirectional measurements are used to determine the inverse distance field (IDF), which is the basis for determining directional field strength. Although the NPRM tentatively rejected a reduction in the required number of close-in measurement points, we recognize that, in many cases, it is not possible for the permittee to take measurements at every specified interval within 3 kilometers of the antenna site. It has been our policy to accept fewer close-in measurements in these circumstances, provided the inverse distance field can be determined with reasonable certainty. We therefore add the stipulation that the close-in measurements include at least seven points to formalize our policy while providing some relief to the broadcaster.
10.DLR, Clear Channel, and Hatfield & Dawson favor a reduction in the number of measured points to ten and the elimination of close-in nondirectional measurements.[9] Instead of determining the nondirectional inverse distance field by graphical analysis, DLR proposes using the theoretical nondirectional field. In support of the proposal, DLR supplies a tabulation of results from 57 proofs accepted by the Commission.[10] We decline to adopt further measurement reductions. While we recognize the merit of this suggestion, our experience has shown that proper detuning of unused towers in an array may be difficult, and that unused towers can significantly distort nondirectional patterns. We continue to believe, along with the majority of commenters, that our proposed reduction in the number of required measurements will provide a sufficient basis for graphical analysis of field strength measurements. We will adopt the proposal to shorten the minimum radial length to 15 kilometers and to require a minimum of 15 points, distributed as set forth above, for full proofs.
11.Many commenters state that the distribution of measurement points should be flexible, so that the engineer may avoid areas where field strength cannot be measured reliably. NAB requests “that broadcasters be given some discretion in designating far-point measurements.” In fact, 47C.F.R.§73.186(a)(1) already provides this discretion, requiring licensees to exercise good engineering judgment in selecting locations for field measurements based on the approximate intervals we establish in this Report and Order.
3. Standard Format for Reporting Measurements
12.We also sought comment on a standard format for reporting field strength measurements. Most applicants already submit field strength measurements in table format using commercial spreadsheet or database software. We proposed to adopt a standardized format for the submission of the data in order to facilitate electronic filing and processing. Electronic storage of this data could also facilitate easy retrieval by any interested party. Nearly all commenters agree that a standard data format would be useful. Potomac Instruments, Inc. presents a sample format which would be compatible with GPS receiver output. In addition, Hammett & Edison suggests that we include a field for measured ground conductivity, since this is the information usually sought by engineers who retrieve field strength measurements. We agree that electronic storage and retrieval of measured conductivities would be useful. Based on the comments received, we will develop a format for submission of field strength measurements and for ground conductivities derived from measurements. We will release the details of these file formats concurrently with the Public Notice releasing the new, revised version of FCC Form 302-AM to be utilized for electronic filing. In a related matter, DLR suggested deleting the requirement to include topographic maps showing each measurement point in a full proof of performance. We agree that this requirement places an unnecessary burden on the AM station. Furthermore, the size of the topographic maps makes it particularly difficult to provide them in electronic format. We will therefore modify our rules to require that licensees retain copies of the topographic maps showing measurement points, to be provided to Commission staff upon request.[11]
B.Partial Proof of Performance
13.Partial proofs of performance are required after the installation of new equipment on an AM tower or where changes in the electrical environment, such as erection of a new tower nearby, could affect the radiation pattern. These proofs are conducted to verify that the array remains properly adjusted. A partial proof consists of measurements taken at selected locations used in the last full proof of performance. The field strength values measured at each point are mathematically compared to values obtained in the last full proof to yield the current value of radiation along each azimuth.
1.Number of Radials Required, Number of Points per Radial
14.Background. Permittees must now make at least ten field strength measurements between three and 16 kilometers from the array at points used in the last complete proof of performance.[12] If a radial contains a monitoring point,[13] that point must be included in the measurements. A partial proof includes measurements on all radials measured in the full proof. We proposed to reduce to eight the required minimum number of points per radial, including any monitor points.
15.Discussion. The Association of Federal Communications Consulting Engineers (AFCCE) points out that, while a full proof is “a rare event” for most AM stations, partial proofs are relatively frequent. Therefore, AFCCE states, “reducing the cost of a partial proof is more important than reducing the cost of a full proof…[and] increases the likelihood that station management will authorize the measurements when the need is indicated.” We agree that reducing the requirements for a partial proof may expedite the process of correcting malfunctioning AM arrays. As proposed in the NPRM, we will reduce the number of points per radial from ten to eight, including any monitoring point on the radial. Further, we will incorporate commenters’ proposals to reduce the number of radials measured. We will limit the radials measured on a partial proof to those radials which include monitoring points.[14] If a directional pattern has fewer than four monitored radials, the licensee should include the nearest adjacent radials from the full proof, for a minimum of four. We believe that these changes will minimize the financial burden on directional AM stations while still providing sufficient data to verify directional array performance.
16.Several commenters note that many partial proofs rely on full proof measurements which may be decades old.[15] Even when a full proof is relatively recent, changes to the area surrounding the AM station may alter propagation characteristics, or may make it impossible to locate points identified in the full proof. In such circumstances the comparison of recent directional measurements with old readings may be invalid. We agree that an alternate approach is warranted. In cases where the engineer cannot identify points from the last full proof with reasonably certainty, or where the environment around the AM station has changed, we will allow the station to select eight suitable points on each radial at which to measure both directional and nondirectional fields. The average ratio of directional to nondirectional field strength may then be used in conjunction with the measured nondirectional field to determine the directional field.[16] Occasionally, licensees performing a partial proof discover that radiation on one or more bearings exceeds the standard pattern, often from changes in the vicinity of the directional antenna which are beyond the licensee’s control. In these circumstances, we will permit the licensee to augment the standard radiation pattern based on the results of full directional and nondirectional measurements on the affected radial, including close-in points in accordance with §73.186. The inverse distance field should be determined graphically, as required in a full proof of performance.[17]
2.When Required
17.Background. A licensee is required to conduct a partial proof of performance when there is some indication that the antenna system may not be operating as authorized, e.g., when monitoring point readings or antenna monitor readings exceed the limits specified on the station's license.[18] The NPRM did not propose to relax this requirement. Currently, 47C.F.R.§73.68 also requires a partial proof when sampling system components mounted on the tower are replaced or modified. We proposed to eliminate the latter requirement provided the new components are mounted in the same location and, where appropriate, with the same orientation, as the old components and: (1) measurements made at the monitoring points before and after installation establish that the substitution had no effect; and (2) antenna monitor values remain within the tolerances specified in the rules or on the station's authorization. If the monitoring point readings or antenna monitor values exceed authorized limits, then a partial proof would be required.
18.Discussion. Allcommenters who address this issue agree that a partial proof should not be mandatory when sampling system components are replaced or modified. With the provisions noted, we will delete the requirement for a partial proof in 47C.F.R.§73.68.